704 research outputs found
Deep XMM Observations of Draco rule out at the 99% Confidence Level a Dark Matter Decay Origin for the 3.5 keV Line
We searched for an X-ray line at energies around 3.5 keV in deep, ~1.6 Msec
XMM-Newton observations of the dwarf spheroidal galaxy Draco. No line was found
in either the MOS or the PN detectors. The data in this energy range are
completely consistent with a single, unfolded power law modeling the particle
background, which dominates at these energies, plus instrumental lines; the
addition of a ~3.5 keV line feature gives no improvement to the fit. The
corresponding upper limit on the line flux rules out a dark matter decay origin
for the 3.5 keV line found in observations of clusters of galaxies and in the
Galactic Center at greater than 99% C.L..Comment: 5 pages, 3 figures, accepted for publication in Monthly Notices of
the Royal Astronomical Society; includes new discussion on Ruchayskiy et al
(2015), arXiv:1512.0721
Exploring A Cosmic-Ray Origin of the Multi-wavelength Emission in M31
A recent detection of spatially extended gamma-ray emission in the central
region of the Andromeda galaxy (M31) has led to several possible explanations
being put forth, including dark matter annihilation and millisecond pulsars.
Another possibility is that the emission in M31 can be accounted for with a
purely astrophysical cosmic-ray (CR) scenario. This scenario would lead to a
rich multi-wavelength emission that can, in turn, be used to test it.
Relativistic cosmic-ray electrons (CRe) in magnetic fields produce radio
emission through synchrotron radiation, while X-rays and gamma rays are
produced through inverse Compton scattering. Additionally, collisions of
primary cosmic-ray protons (CRp) in the interstellar medium produce charged and
neutral pions that then decay into secondary CRe (detectable through radiative
processes) and gamma-rays. Here, we explore the viability of a CR origin for
multi-wavelength emission in M31, taking into consideration three scenarios: a
CR scenario dominated by primary CRe, one dominated by CRp and the resulting
secondary CRe and gamma rays from neutral pion decay, and a final case in which
both of these components exist simultaneously. We find that the multi-component
model is the most promising, and is able to fit the multi-wavelength spectrum
for a variety of astrophysical parameters consistent with previous studies of
M31 and of cosmic-ray physics. However, the CR power injection implied by our
models exceeds the estimated CR power injection from typical astrophysical
cosmic-ray sources such as supernovae.Comment: Accepted to Phys Rev D, 15 Pages, 9 figures, 4 tables, updated
figures/tables, added discussio
Tesla Solar Roof
The roof tiles are actually made of textured glass. From most viewing angles, they look just like ordinary shingles, but they allow light to pass through from above onto a standard flat solar cell. These roofs should far outlast the standard 20-year life cycle common for roofing materials used today and are able to power a strandard home.https://openscholarship.wustl.edu/bcs/1237/thumbnail.jp
The use of recombinant DNA technology in producing pharmaceuticals
Rekombinantna DNA tehnologija podrazumijeva metode kojima možemo prenijeti gene iz jednog organizma u drugi. Time se omogućava dobivanje proteina u organizmima u kojima se ti proteini prirodno ne stvaraju. Takva tehnologija danas ima brojne primjene, a jedna od njih je proizvodnja lijekova. Prvi ljudski protein dobiven iz bakterije E. coli bio je inzulin, 1982. godine. Danas se za manipulaciju gena u svrhu dobivanja rekombinantnih proteina, osim bakterija, koriste i kvasci, životinje, biljke te stanične kulture. Svaka metoda proizvodnje ima svoje prednosti i nedostatke. Glavni nedostatak bakterijama je nemogućnost glikozilacije proteina. Kvasci, kao eukarioti, uspješniji su u tom procesu. Transgenične životinje mogu izlučivati znatne količine proteina u krv, mlijeko, bjelanjak ili urin. Mogu proizvoditi proteine složenih struktura koji moraju proći proces posttranslacijske modifikacije da bi postali aktivni. Upotreba transgeničnih životinja postavlja brojna etička pitanja te pitanja vezana uz sigurnost pripreme takvih proteina. Transgenične biljke mogu proizvoditi velike količine proteina te stvarati proteine kompleksnih struktura. Također takva je proizvodnja jeftina i nema gotovo nikakvih etičkih problema. Najveći nedostatak genetički modificiranih organizama je interakcija s okolišem. Unatoč tome što još uvijek malo znamo o tome kakav bi učinak transgenični organizmi mogli imati na svoj okoliš, možemo reći da je rekombinantna DNA tehnologija u proizvodnji lijekova svojevrsno čudo 20.-og stoljeća.Recombinant DNA technology encompasses various techniques by which we can transfer genes from one organism to another. This way we accomplished production of proteins in organisms for which these proteins are not natural. Such technology has many applications today. One of them is the use in producing pharmaceuticals. Proteins play an important role in the pharmaceutical industry. The first human protein produced in Escherichia coli was insulin, in 1982. Today, we use biotechnology in order to obtain recombinant proteins from bacteria, yeasts, animals, plants and cell cultures. Each manufacturing method has its advantages and disadvantages. The major drawback of bacteria is that they are unable to perform the posttranslation modifications such as glycosylation. Yeasts, as eukaryotes, have some advantages over bacteria in this process. Transgenic animals can secrete significant amounts of protein in blood, milk, egg white or urine. They can also produce proteins with complex structure that must undergo a process of posttranslational modifications. The use of transgenic animals faces many ethical issues and issues of environmental impact of such animals. Transgenic plants can produce large amounts of protein and they can also form complex protein structures. This system of production is cheap and avoids some ethical issues. The biggest disadvantage is interaction with the environment. Although we still know little about how transgenic organisms could affect the nature one day, we can say that the recombinant DNA technology in the production of pharmaceuticals is sort of a miracle of the 20th century
Multiwavelength Analysis of Dark Matter Annihilation and RX-DMFIT
Dark matter (DM) particles are predicted by several well motivated models to
yield Standard Model particles through self-annihilation that can potentially
be detected by astrophysical observations. In particular, the production of
charged particles from DM annihilation in astrophysical systems that contain
magnetic fields yields radio emission through synchrotron radiation and X-ray
emission through inverse Compton scattering of ambient photons. We introduce
RX-DMFIT, a tool used for calculating the expected secondary emission from DM
annihilation. RX-DMFIT includes a wide range of customizable astrophysical and
particle parameters and incorporates important astrophysics including the
diffusion of charged particles, relevant radiative energy losses, and magnetic
field modelling. We demonstrate the use and versatility of RX-DMFIT by
analyzing the potential radio and X-ray signals for a variety of DM particle
models and astrophysical environments including galaxy clusters, dwarf
spheroidal galaxies and normal galaxies. We then apply RX-DMFIT to a concrete
example using Segue I radio data to place constraints for a range of assumed DM
annihilation channels. For WIMP models with GeV and
assuming weak diffusion, we find that the the leptonic and
final states provide the strongest constraints, placing limits
on the DM particle cross-section well below the thermal relic cross-section,
while even for the channel we find limits close to the thermal relic
cross-section. Our analysis shows that radio emission provides a highly
competitive avenue for dark matter searches.Comment: 21 pages, 9 figures, 2 tables, corrections to figures, additional
text, accepted to JCA
Synchrotron Emission from Dark Matter Annihilation: Predictions for Constraints from Non-detections of Galaxy Clusters with New Radio Surveys
The annihilation of dark matter particles is expected to yield a broad
radiation spectrum via the production of Standard Model particles in
astrophysical environments. In particular, electrons and positrons from dark
matter annihilation produce synchrotron radiation in the presence of magnetic
fields. Galaxy clusters are the most massive collapsed structures in the
universe, and are known to host G-scale magnetic fields. They are
therefore ideal targets to search for, or to constrain the synchrotron signal
from dark matter annihilation. In this work we use the expected sensitivities
of several planned surveys from the next generation of radio telescopes to
predict the constraints on dark matter annihilation models which will be
achieved in the case of non-detections of diffuse radio emission from galaxy
clusters. Specifically, we consider the Tier 1 survey planned for the Low
Frequency Array (LOFAR) at 120 MHz, the EMU survey planned for the Australian
Square Kilometre Array Pathfinder (ASKAP) at 1.4 GHz, and planned surveys for
APERTIF at 1.4 GHz. We find that, for massive clusters and dark matter masses
GeV, the predicted limits on the annihilation cross section
would rule out vanilla thermal relic models for even the shallow LOFAR Tier 1,
ASKAP, and APERTIF surveys.Comment: accepted to ApJ; removal of LOFAR Tier 2 limits; other minor text
changes; conclusions largely unchange
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